The present invention relates to a primer composition. More particularly, the invention relates to a primer composition which can be dried at ambient temperature to form a strong and transparent coating or film on the surface of a substrate, provide excellent adhesion between the substrate and a silicone elastomer, and which can be used effectively as a primer.
A means which is often employed for bonding a room temperature-curable silicone elastomer to a substrate is to treat the substrate in advance with a primer and then apply the room temperature curable silicone elastomer thereto. One of the main uses of a room temperature curable silicone elastomer is as a sealant, for example, in construction. Anodized aluminum, because it is lightweight and exhibits excellent weatherability and colorfastness, is often used as an exterior wall of a building to which silicone elastomer must be bonded. It has been suggested that silicone elastomer has inferior adhesion to anodized aluminum than conventional aluminum materials such as (surface-oxidized-- aluminum, acrylic resin coated aluminum and duralumin. Also, in the case of anodized aluminum, satisfactory adhesion cannot be obtained regardless of the primer used. Because anodized aluminum is often used in combination with conventional construction materials such as mortar, concrete, precast concrete (PC), autoclaved light concrete (ALC), marble and granite, a suitable primer must exhibit good adhesion not only to the anodized aluminum but also to these conventional materials. Moreover, since anodized aluminum is frequently used in combination with coated metals, stainless steel, plastics and glass, good adhesion to these materials is also required. However, because there has not been present a primer having good adhesion to all of the above-mentioned materials, there is often adopted a method in which different primers are used for each of the respective materials so as to obtain satisfactory adhesion. However, such an operation is very complicated. Therefore, development of a primer having good adhesion to all of the materials to be bonded is very desirable.
Satisfactory primers have been developed for conventional construction substrates, but a primer having good adhesion not only to anodized aluminum but also to other materials to be bonded has not heretofore been developed.
Japanese Patent Application Laid-Open Specifications No. 158499/79 and No. 50979/81 already disclose a silane-modified resin obtained by reacting a resin formed by introducing an epoxy group and a hydroxyl group (which may be partially esterified) into a homopolymer of 1,3-pentadiene or a copolymer of 1,3-pentadiene with another monomer, having an iodine value of 200 to 500 and an average molecular weight of 350 to 10,000, with a carbon-functional silane as one component of a primer. As the other component of the primer, a mixture of a chlorinated polymer and an organic polyisocyanate or an acrylic resin, a polyurethane resin or a mixture thereof is used. Accordingly, these primer compositions are insufficient in the resistance to heat, ozone, ultraviolet radiation and weathering. When these primer compositions are used with a silicone sealant having the highest durability among known sealing compounds, the bonding capacity cannot be maintained for a long time and the bonding strength is limited. Moreover, these primer compositions are insufficient in their bondability to colored anodized aluminum which is considered most difficult to bond.
We conducted research with a view towards developing a primer composition free of the foregoing shortcomings, and, as a result, have found that a primer composition obtained by adding a mercapto group-containing silane, an amino group-containing silane and a silicon compound or a partially hydrolyzed condensate thereof to the above-mentioned known silane-modified resin is excellent in bondability or adhesion to anodized aluminum and has good bondability to materials such as mortar or concrete, metals such as steel or stainless steel, paints comprising an acrylic resin or epoxy resin as a vehicle and glass.
The present invention has now been completed based on this finding, and it is a primary object of the present invention to provide a primer composition capable of imparting excellent adhesion or bondability between a silicone elastomer and conventional construction substrates as well as anodized aluminum.